This invention generally addresses a communications system in which a plurality of spacially separated devices utilize RF communications and more specifically addresses a method for selecting the best antenna pattern from among several choices of antenna patterns. This invention is especially suited for, but not limited to, an environment in which multipath signals and fading problems are significant such as in an RF communication system located inside a building.
It is generally known that directive antenna patterns can be utilized to enhance RF communications between remote RF transceivers. It is also generally known that various means exist for controlling an antenna radiation pattern such as by rotating a highly directional antenna, controlling the phasing of different antenna elements to electronically steer the primary beam or radiation pattern, and the selection of different directional antennas targeted at different locations.
Methods for selecting an optimal antenna pattern vary greatly depending upon the environment. In microwave line of sight communication applications, the antenna pattern selection is simple: just orient highly directional antennas pointing at each other. Physically separated antennas may be utilized by an RF transceiver to enhance communications that are not line of sight. In such diversity applications each antenna may be monitored with the antenna having the optimal signal being selected for use of all of the antennas may be combined utilizing the proper phasing to generate an enhanced single signal.
A number of factors make the problem of antenna pattern selection difficult. The reception of multipath signals, i.e. receiving the same signal at different times with different signal strengths from different geographic locations, greatly complicates antenna pattern selection. The constant fading of signals also adds to the problem. These factors are present inside a building in which RF transceivers communicate using the 1-20 GHz (gigahertz) frequency range. The relatively close distances between the antennae and reflectors, such as walls, floors, ceilings and other metal objects large relative to the wavelength, result in strong multipath signals. Continuous fading results from environmental changes such as the movement of people. There exists a need for an antenna pattern selection method which optimizes communications in such an environment.